1. Field of the Invention
The present invention relates to a digital power meter apparatus and method for the same, more particularly to a digital power meter apparatus using multipliers and adders arranged in a plurality of stages and method for the same.
2. Description of Prior Art
To calculate the watt consumption for a household user, the prior art electrical power meter generally uses an inductive-type AC ampere meter to calculate the used current. However, the prior art electrical power meter uses mechanical wheel driven by gear to count the ampere used, the electrical power meter using mechanical wheel has problem of erroneous measurement due to manufacture tolerance and teeth ratio variation. Moreover, the prior art electrical power meter is sensible to temperature variation, which causes problem for users distribute at wide area and reduce lifetime of this power meter. This correct watt measurement causes inconvenience both to client and power company.
The electrical power meter has a trend of digitalization as the progress of electrical industry and digital technology. For example, Taiwan patent gazette No. 482901 discloses a digital AC power meter. The disclosed digital AC power meter uses optical signal for outputting digital measurement and sends output through network. However, this digital AC power meter still uses mechanic wheel to count the used current. The precision thereof is still an issue.
Moreover, U.S. Pat. Nos. 5,862,069, 5,745,323, 5,872,469 and 5,760,619 had disclosed related art. More particularly, the U.S. Pat. No. 5,862,069 discloses a power meter and related method using four quadrant, multiplied signal. In this power meter, a first input signal from a dual input channel is processed by a low-pass filter and an interpolator for producing an output signal. The output signal is then multiplied with a second input signal by a multiplier to produce a digital power signal. Moreover, the digital power signal is processed by a low-pass filter to produce an output digital power signal, which accounts for power consumption. The power meter disclosed in this patent has more precise measurement result than the prior art inductive type power meter.
However, the above-mentioned power meter performs signal process for only one input signal and the signal process involves only one multiplication process. The above-mentioned power meter has still limited and unsatisfactory precision. If the used electrical power cannot be precisely measured, it is troublesome for both power company and user.